Web 2.0 and AJAX Security. OWASP Montgomery. August 21 st, 2007

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1 Web 2.0 and AJAX Security OWASP Montgomery August 21 st, 2007

2 Overview Introduction Definition of Web 2.0 Basics of AJAX Attack Vectors for AJAX Applications AJAX and Application Security Conclusions 1

3 Introduction Dan Cornell Principal of Denim Group, Ltd. Software developer by training and background JEE.NET A little bit of everything else Currently focused on security Application assessments and penetration tests Training and mentoring Look at both building and breaking web applications 2

4 Definitions of Web 2.0 Evangelical Technical 3

5 Definition of Web 2.0 (Evangelical) Web 2.0 is the business revolution in the computer industry caused by the move to the internet as platform, and an attempt to understand d the rules for success on that t new platform. Chief among those rules is this: Build applications that harness network effects to get better the more people use them. -Tim O Reilly 4

6 Definition of Web 2.0 (Technical) Collaborative Applications New Technologies AJAX Flash/Flex Rich Internet Applications UI is more interactive Key to remember: HTTP requests are still just bits transmitted across the wire 5

7 Basics of AJAX Asynchronous JavaScript and XML Term coined by Jesse James Garrett Illustrations from next two slides come from this URL Relies on the XMLHttpRequest object accessible from JavaScript Security model only allows the browser to connect back to the original server These techniques have been around for a while but have only recently seen wide adoption 6

8 AJAX Illustrated 7

9 AJAX Illustrated 8

10 What Does AJAX Look Like? Still bits going across the wire Still HTTP traffic Headers GET parameters POST data Content is typically different than normal HTTP traffic XML JSON (versus HTTP POSTs and HTML) 9

11 What Does AJAX Look Like? 10

12 What Does AJAX Look Like? 11

13 Why is AJAX Security a Concern? Web 2.0 application have all the same problems as traditional web applications and more! Threat models / risk profiles are not well understood Focus on what CAN be done not what SHOULD be done Practitioners are focused on what they can do rather than how (or if) they should do it 12

14 Attack Vectors for AJAX Applications Front-door attacks on server-side resources Remote control attacks via target application Remote control attacks via 3 rd party application 13

15 Attack Vectors for AJAX Applications Front-door attacks on server-side resources SQL injection attacks AuthX, AuthZ attacks 14

16 Attack Vectors for AJAX Applications Remote control attacks via target application Cross Site Scripting (XSS) Cross Site Request Forgery (CSRF) 15

17 Attack Vectors for AJAX Applications Remote control attacks via 3 rd party application JavaScript manipulation 16

18 Fundamentals of AJAX Security All the standard rules for web application security still apply Perform Threat Modeling / Risk Assessment Validate input: Do not trust anything in the request Cookies, other HTTP Headers Parameters Prefer positive validation to negative validation Escape output HTML (HTMLEncode) XML (XMLEncode) URL parameters (URLEncode) Authentication and Authorization still matter Web services and other Web 2.0 endpoints must require authentication and should enforce authorization 17

19 Fundamentals of AJAX Security New things to think about Protect methods to access sensitive URLs Prefer POST requests over GET requests There are lots of ways to make GET requests (<IMG> <SCRIPT> and so on) POST requests are typically only automated via XMLHttpRequest Know what hosts serve what content Be careful what you send via JavaScript Sensitive data may be accessible off-domain 18

20 Some (In)Famous Vulnerabilities MySpace Worm GMail Hacks 19

21 MySpace Worm Based on an assembled JavaScript built up from several substrings Bypassed numerous negative filters against malicious tags, attributes, etc Relied on the same functionality being served from multiple hostnames profile.myspace.com and Used a multi-step background combination of GETs and POSTs Get the list of friends Parse out special POST tokens Add samy as a new friend For more info: Technical explanation: / l /t h l 20

22 MySpace Worm: Lessons Learned Better input validation positive versus negative where possible Interpretable HTML is a big place so carving out a couple of tags or syntax bits will not remove the ability of attackers to find workarounds Be careful about what functionality is available from where GETs versus POSTs What applications are available from a given hostname? Similar to checking to be sure that HTTPS content is not available via HTTP 21

23 GMail Hacks Link to malicious site sent in GMail message User clicks on link and page renders Page contains a script reference to a Gmail URL that will render sensitive data encoded in JavaScript User s cookies are sent along to GMail because user was just logged in to GMail Page also contains an override for the JavaScript Array() constructor Browser can then access off-domain JavaScript content and send along to a 3 rd party site More information: Easier to type: 22

24 GMail Hacks: Lessons Learned Do not put sensitive data in JavaScript content in a form that can be automatically parsed What if it ends up in a SCRIPT tag? Possible to override constructors in JavaScript language URLs that render JavaScript with sensitive data should be hard to get to (for an attacker) POST rather than GET Unpredictable URL Check referrers Can be spoofed but can help prevent execution in some cases 23

25 AJAX and Application Security Old Favorites Authentication and Authorization SQL Injection Cookie Tampering Parameter Tampering New Stuff Additional State on the Client Cross Site Scripting Cross Site Request Forgery (CSRF) JavaScript Manipulation 24

26 Old Favorites Authentication and Authorization SQL Injection Cookie Tampering Parameter Tampering 25

27 Authentication and Authorization XMLHttpRequests send along the same cookies as the browser Leverage the server-side session Require authentication as with accessing any other web application Require authorization before allowing access to sensitive content or capabilities Continue to leverage platform Authentication and Authorization features 26

28 SQL Injection This works just like it does for normal web applications Creating SQL queries based on static text and unfiltered inputs 27

29 Cookie Tampering Cookies are passed along with AJAX XMLHttpRequests Can piggyback of pre-existing session login Malicious users can still modify cookies when making direct requests 28

30 Parameter Tampering Parameters are passed along with the XMLHttpRequests via a variety of means GET POST Each framework has its own encoding scheme 29

31 New Stuff Additional State on the Client Cross Site Scripting (XSS) Cross Site Request Forgery (CSRF) JavaScript Manipulation XML Security JSON Security 30

32 Additional State on the Client Bad in normal web applications Hidden FORM fields Cookies TERRIBLE in AJAX applications Although handling things on the client is kind of the point of AJAX No excuse for sloppy server-side validation 31

33 Cross Site Scripting Receiving HTML from 3 rd party sites is just as dangerous to AJAX-enabled applications How much do you trust the folks you are talking to? Standard threat modeling applies 32

34 Cross Site Request Forgery (CSRF) Similar to Cross Site Scripting (XSS) Inject HTML or JavaScript to make rogue requests XMLHttpRequest calls <img src= Risk mitigation: Limit URLs to only render for POST requests Helps prevent access via IMG tags and the like Add nonces to URLs Require ViewState encryption/validation on ASP.NET sites 33

35 JavaScript Manipulation AJAX applications often render our JSON or other valid JavaScript These can be potentially accessed via 3 rd party sites Sensitive data can be retrieved and sent elsewhere Risk Mitigation Do not send sensitive data in JavaScript parsable format Might end up in a <SCRIPT> tag It is possible to defeat built-in browser protections for JavaScript security Redefine JavaScript Array() constructor t Redefine JavaScript object() constructor 34

36 XML Security If clients are sending XML documents be careful what you trust DOM SAX Text on network wire is turned into objects in server memory Potential for DoS attacks by consuming memory <tag /><tag /><tag /> XML documents passed between systems can be injected just like SQL Watch out for re-occurrence of tags Application expects <tag1 /><tag2 /> Application sees <tag1 /><tag2 /><tag1 /> 35

37 JSON Security JSON can be made into JavaScript objects using the eval() command This is dangerous Use parsejson() function instead 36

38 OWASP and Web 2.0 Security Open Web Application Security Project (OWASP) OWASP AJAX Project OWASP Sprajax Project OWASP Testing Guide 37

39 Contact Dan Cornell (210) Website: Blog: 38

Information Security CS 526 Topic 8

Information Security CS 526 Topic 8 Web Security Part 1 1 Readings for This Lecture Wikipedia HTTP Cookie Same Origin Policy Cross Site Scripting Cross Site Request Forgery 2 Background Many sensitive